msm: vidc: Ignore bus votes with no load

Previously, votes of zero load picked up the lowest non-zero vector in
the bus table.  This leads to minute, unnecessary votes on behalf of
video instances of other types that don't really exist.

Just ignoring the vote altogether gives us some minor power savings.

CRs-Fixed: 657690
Change-Id: I0c2cb19db35cea64f43e61fae7d4ca85b93b4c85
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>